Micro-controller help... or something

I'm building a circuit out of a cheap (9)5mm LED flashlight. The LEDs are wired in parallel and the original circuit didn't even have a resistor. How this works I have no idea, something about the 3 AAA batteries acting as resistors themselves. Anyway, I need to find a driver, micro-controller, or something, that can:

provide a constant current
pwm to increase run time
detect darkness
provide low voltage cut off to protect my Li-ion batteries

I've been racking my brain and I'm pretty sure I've searched the entire internet for something that can get the job done. Did I mention that it needs to be super cheap?

Thanks for any help you can offer.

Look at this: http://ledcalc.com/ or this: http://led.linear1.org/led.wiz and you will see that 9 parallel white LED's each need a resistor of 68 ohm to function properly.
Fv LED ± 3.2V, 3x AAA = 4,5 V so you blow your LED's when parallel connected (with 2 cells you could connect them directly =3V)

Yeah, I've been told that LEDs need a dedicated resistor. Eventually I would like to replace the 9 5mm LEDs with a HPLED but i don't want the 350ma draw. I figure if I send about 135ma through the circuit each LED will get about 15ma and the ones that draw more will simply draw around 20ma. I might be completely wrong about this so if anyone has any suggestions please feel free to tell me. Thanks for the reply.

Hello drew12,

You Don't draw 350 mA with those 9 LEDs but around 170 mA, see the calculation I did with your 9 LEDs and 4,5 V from 3 cells.
I recently build a light with 36 LEDs! on a surface of round 40 mm, see pictures on the same link as the calculation is

drew12 said:

I'm building a circuit out of a cheap (9)5mm LED flashlight. The LEDs are wired in parallel and the original circuit didn't even have a resistor. How this works I have no idea, something about the 3 AAA batteries acting as resistors themselves. Anyway, I need to find a driver, micro-controller, or something, that can:

provide a constant current
pwm to increase run time
detect darkness
provide low voltage cut off to protect my Li-ion batteries

I've been racking my brain and I'm pretty sure I've searched the entire internet for something that can get the job done. Did I mention that it needs to be super cheap?

Thanks for any help you can offer.

Click to expand...

you need to be a little bit more specific about your requirements .. does it need to run on those 3 AAA batteries?
is the constant current for some critical light level?
pwm to increase run time ... how long does it need to run?
detect darkness .. total darkness or some threshold low light level?
what batteries are you using?
define super cheap?
how much electronics skill do you have?
how small of a package does it need to be in?

many of the Atmega chips are cheap and will do voltage sensing (to detect light level and battery voltage) and PWM to pulse a control signal to a transistor switch for your lights. Programming it would require one of the many arduino boards ($30-60 range) and some free software, but relatively easy to do.
dmac386

I've found some ready made charging circuits that are not too expensive. Something like $1.50 for a li-ion solar charger is perfect. Now, hopefully I will not have to program it or anything.